Process and device for the continuous concentration-crystallization of sugar syrups



P 7, 1970 J. M. MALEK 3,505,111

PROCESS AND DEVICE FOR THE CONTINUOUS CONCENTRATION-CRYSTALLIZATION OF SUGAR SYRUPS Filed Feb. 4, 1965 2 Sheets-Sheet 1 April 7, 1970 J. M. MALEK 3,505,111

PROCESS AND DEVICE FOR THE CONTINUOUS CONCENTRATION-CRYSTALLIZATION OF SUGAR SYRUPS Filed Feb. 4, 1965 2 Sheets-Sheet 2 United States Patent 16 Claims ABSTRACT OF THE DISCLOSURE A process for the continuous concentration-crystallization of sugar syrups and massecuite by evaporation. The process comprises continuously subjecting syrups supplied in a continuous manner to a series of successive crystallizing steps under the action of heating and boiling in several successive crystallizing mass (i.e. massecuite) recirculation circuits, introducing directly into the crystallizing mass, during each of the crystallizing steps, except the first one, a damp air gaseous phase to ensure intense agitation and circulation of the said crystallizing mass in said successive recirculation circuits, separating the gaseous phase released by the massecuite at the top of each recirculation circuit, recycling by gravity the massecuite separated from the gaseous phase at the head of each recirculation circuit, so that each recirculation circuit has two liquid columns connected to their heads and bottoms, the massecuite in one of said liquid columns having an upward movement caused by the thermic currents resulting from heating and from gaseous phase bubbles rising in said column, while the massecuite in the associated recycling column has a downward movement, interconnecting two successive circuits, and discharging at the end of said successive crystallizing steps the product composed of nearly uniform crystalline grains in suspension in the resulting molasses.

In the sugar industry, it is known that the final concentration by vacuum boiling of syrup, which is a sugar solution preconcentrated by evaporation, is carried out batchwise and that this batch type operation is often the cause of a bottleneck in the sugar production because complementary operations in this production are generally effected in continuous manner.

It is also known that this industry is interested in the production of the most uniform sugar crystals in suspension in mother-liquors, the mother-liquors being called molasses and such mixture of sugar crystals and molasses being called massecuite, while the molasses are a form of sugar syrups. It is further known, however, that from one boiling operation to another the crystal sizes vary which, in consequence, gives a non-homogeneous final product.

Besides, in the course of a single boiling operation in a vessel of a known type, the crystals produced are not generally uniform, because of the existence of areas with different syrup and massacuite agitation intensities in the vessel, these differences involving different crystal developments.

To make the sugar syrup and massecuite agitation stronger and identical throughout each boiling vessel, attempts have been made to employ mechanical agitators and circulation pumps, but the utilization and the maintenance of these devices is difficult and expensive.

Another disadvantage of conventional equipment is the ice low heat transfer through the heating walls which are generally composed of short vertical tubes heated by steam.

This small heat exchange is due, on the one hand, to the slow massecuite circulation about the end of the boiling operation and, on the other hand, to the fouling which is produced consequently to the syrup and massecuite evaporation and partial decomposition on the heating surfaces, this decomposition being also a result of action of reducing sugars and amino acids present in the sugar syrups, and a source of coloration which lowers the quality of the product.

The main object of the present invention is to provide for avoiding these inconveniences by establishing a plant wherein the sugar syrup boiling process can be carried out under continuous working conditions, wherein the syrup or the massecuite will be subjected to an intense and relatively uniform mixing, and wherein the fouling of the heating surfaces will be avoided.

According to the present invention, the sugar syrup to be concentrated and crystallised is supplied in continuous manner and subjected to a series of continuous successive unit heatings and to corresponding evaporations. As a rule, during each of the resulting crystallizations, a gaseous phase, such as air, relatively compressed and preferably saturated with steam, is introduced into the syrup or massecuite. The rising gaseous bubbles including the steam are preferably subjected to a forced dispersion (i.e. subdivision) for obtaining smaller bubbles in order to ensure an efficient mixing as well as syrup or massecuite rising; after this gaseous phase has passed through the fluid column of said syrup or massecuite, the former is separated at the head of this fluid column and the syrup or massecuite is allowed to flow down by gravity, thus creating a recirculation circuit for each evaporationcrystallisation. Each recirculation circuit thus created is supplied, but as a rule except for the last recirculation circuit of the series, with sugar syrup, in order to compensate for the consumption due to the treated syrup evaporation and crystallisation, and the product composed by uniform sugar grains in suspension in the molasses is discharged in continuous manner at the end of the series of successive heatings-evaporations crystalizations.

A device to be used to perform this process consists of a series of evaporating-concentrating-crystallizing vessels, called units, each one of said units comprising a first substantially vertical column heated in its lower part, where the hydrostatic-pressure exerted by the column content is sufiiciently high to avoid the ebullition of the syrup in this heated part, said column ending at its head in a liquid-vapor separation chamber connected with the base of the first column through a second column serving as a downcomer for recirculation of the boiling mass from said chamber. The first column contains, in its upper part an expansion chamber for the syrup or massecuite arriving hot from the heated part of the column and at the head of this expansion chamber, a device for the forced dispersion of the steam and gaseous phase bubbles which are introduced and distributed into the syrup or the massecuite under the level of this device. Said dispersing device is formed by a plurality of vertical partitions, allowing a free passage for the boiling mass between them massecuite in the column, while the introducing and distributing means consists generally of a bubbler. The first evaporating crystallising unit comprises an inlet for the continuous supply of syrup to be treated and might be provided with a proportioning device of crystalline germs known as crystallization seed. The last unit comprises a continuous outlet of the massecuite forming the product of the operation and each of said units comprises an inlet for massecuite coming from a previous unit, an outlet of the more concentrated massecuite for feeding a following unit, and an inlet for the syrup at a relatively lowrate to compensate for the consumption of said syrup due to evaporation and crystallization.

The above described construction of said units allows the generation of an important motive power for circulation of the syrup or the massecuite circulation, because the fluid content of the first column of the unit comprising numerous rising gaseous phase bubbles has an average specific gravity much lower than the specific gravity of the syrup or of the massecuite in the recirculation column, thus resulting in a considerable difference between the hydrostatic pressures exerted by the two fluid columns. Further a hydraulic hammering which is the stroking of pressure waves in the handled fluent material against a solid surface, such hammering being harmful to the development of uniform sugar crystals is thus prevented.

Besides, the lack of syrup ebullition in the heated part of the first column prevents any change of the concentration of said syrup in the heated area, and, in consequence, substantially suppresses the danger of fouling the heating surfaces, while reducing the thermic decomposition rate. The reduction of the thermic decomposition resulting also from lowering the boiling point (temperature) of the massecuite crossed by air, since the pressure of the formed vapors is the sum of the partial pressures of steam and of air.

Until presently, it was generally thought that the introduction of a gas into a liquor, where a suitable crystal development is required, is harmful for said liquor because it gives rise to the formation of crystalline germs at the liquor-gaseous bubble interface and to the production of crystals of various sizes. It appears then that if the gas, such as air, before its introduction into the liquor, is saturated with the vapors of said liquor and at a temperature equal to or slightly greater than or close to, the liquor temperature, there is no concentration of liquor at the bubble interface, and therefore, the danger of production of non-uniform crystals is reduced.

On the other hand, when the air is introduced into the heated sugar syrup or massecuite, the resulting oxidation of the reducing sugars prevents an excessive coloration of the product and thus improves its quality.

Thus, the process is conformity with this invention will use as the gaseous phase to be introduced into the content of the unit which is part of the boiling device, steam containing air and relatively compressed, in order to gen erate, in the unit, a fluidized bed formed by the sugar crystals, air, steam and molasses, the apparent average viscosity of this fluidized bed being much lower than the viscosity of the highly viscous massecuite in a conventional process, this decrease in viscosity resulting in improved circulation of the boiling mass.

It is obvious that during the running of the apparatus, the period of stay of the treated syrup in a unit will be smaller when the number of these units is higher, and that the crystals leaving, in the concentrated syrup or massecuite, each crystallizing unit will only be of the size they may have reached during the short period of their stay in the unit. If the quantity of units is sufficiently high, the difference between the sizes of the crystals leaving each unit will be relatively small and could be maintained within the required standards.

The description which follows with reference to the accompanying nonlimitative exemplary drawings will give a clear understanding of how the invention can be carried into practice.

In the drawings:

FIGURE 1 is a diagrammatic section of a continuous boiling device for sugar syrups, composed of n evaporating-crystallizing units.

FIGURE 2 is an example of possible realisation of 4 a unit making part of a device similar to that of FIG- URE 1.

FIGURE 3 is a diagrammatic sectional view of a plant conforming to the invention and formed of four units.

FIGURES 4, and 6 are diagrammatic cross-sections of three embodiments of a device for vapor and gaseous phase bubble dispersion formed by a plurality of vertical partitions located in the first column of the unit conforming to the invention.

According to FIGURE 1, each concentrating-crystallizing unit forming part of a boiling device according to the invention and including it units is composed of a first cylindrical column 1a, 1b 1n containing, in its lower part, a heating enclosure formed by a shell 2a, 2b 2n with a bundle of vertical tubes 3a, 3b 3n fixed in plates 4a, 4b 4n and, in its upper part, a plurality of vertical partitions 5a, 5b 5n of a kneed chamber 6a, 6b 6n made in one or several sections, and of a second cylindrical recycling column 7a, 7b 7n connecting said chamber through a recycling kneed element 8a, 8b 8n with the base of the first column. An inlet 9a is used to feed the first unit with fresh syrup to be treated and inlets 9b 9n are used to introduce into each unit the boiled mass coming from the previous unit in the series. An inlet 10b in each unit intermediate the first and the last one of the series allows to feed this intermediate unit with fresh syrup to compensate for the consumption of the treated syrup transformed into vapors and into crystallized product. An outlet 11a, 11b Iln is intended for exhausting vapors to conduit 12, and an outlet 13a, 13b 1311 allows the discharge of each unit or the continuous removal of the boiling mass produced. Inlets and outlets 14a, 14b 14a ensure the inlet of the heating steam and the removal of condensate obtained.

Tubular bubblers 15b 1512 located beneath the heating enclosures, except for the first unit, are used for the introduction of steam saturated air.

The unit illustrated in FIGURE 2 has a shape somewhat diiferent from that of the units of FIGURE 1. Its heating enclosure comprises a shell 16 with tubes 17 fixed in plates 18, is provided with an inlet and an outlet 19 for the feeding and the discharge of the heating fluid and is inclined with respect to the vertical line. On the other hand, the bubbler 20 for introducing relatively compressed damp air is located above said heating enclosure in the unit, and the first column of said apparatus is flared at its upper part 21 in which it contains a plurality of partition walls 22 to help the dispersion of the upstream gaseous phase bubbles. Said upper part 21 of the first column ends at the top by a chamber 23 integral with said upper part, this chamber being useful for the separation of gaseous phase, syrup or massecuite and comprising an outlet 24 for the exhaust of separated gaseous phase. A pipe 25 is used to feed the unit with massecuite coming from another unit (not shown in the drawing) and a pipe 26 is used as an outlet for the concentrated massecuite to move to a following unit in the series (not shown in the drawing). Inlet 27 and outlet 28 allow the introduction of syrup for compensating respectively the consumption in evaporation plus crystallization and the discharge of the apparatus.

The installation illustrated in FIGURE 3 comprises four units. Each of said units comprises a cylindrical column 29a to 29d containing at its axis a recycling tube 30a to 30d opened at its two ends. The lower end of said tube is narrowed and located in the substantially conical bottom area of the column 29a to 29d. This central tube crosses, in the upper part of the column, the heating enclosure 31a to 31d comprising a bundle of vertical tubes 32a to 32d fixed in plates 33a to 33d connected to conduits 34a to 34d and 35a to 35d for the respective supply and discharge of the heating fluid. Right beneath the upper aperture of recycling tube 30a to 30d is situated an assembly of a plurality of vertical partitions 36a to 36a of the type shown in FIG- URE 4. A bubbler 37a to- 37d is arranged in the column below the heating enclosure and is connected to pipes 38a to 38d for the inlet of damp and relatively hot air under a pressure higher than the hydrostatic pressure exerted by the content of the column at the bubbler level. Pipes 39a, 39b and 39c are used for the transfer of the massecuite of a unit to the following unit while a pipe 39d is utilized for the discharge of the contents of the last unit. Pipes 40a to 400 connected to each unit, excepted to the last one in which a closing up namely a final concentration of the massecuite must take place, assure the feeding with compensation syrup, and the pipes 41a to 41d allow the exhaust of vapors. A pressure controller 42 enables to apply in the two first units of the device a constant running pressure higher than that existing in the two other unit vessels.

A proportioning device 43a connected to the first unit is used for the introduction of crystalline germs of determined size into said first unit so as to start the production of uniform crystals in the intstallation.

The level 44a to 44d of the syrup or of the massecuite in each unit of the series during the running of the installation must be situated above the level of the assembly of vertical walls 36a to 36:1 in order that the running efiiciency should be a good one.

The set of substantially vertical partitions as illustrated in FIGURE 4 comprises several walls forming cylindrical sections of different diameters. These sections are joined concentrically by means of flat irons 45 welded, on the one hand, to the upper edges of theses sections and, on the other hand, to the end of the recycling tube 301: to 30d of the unit vessel.

According to the realisation of the assembly of vertical partitions shown in FIGURE 5, said assembly is formed of seven parallel fiat planes 5 fixed between each other by means of stayed and bolted tie-rods 46, this set can be suspended in the upper part of the first column of the unit by means of lugs 47.

The assembly of substantially vertical partitions illustrated in FIGURE 6 comprises several undulated sheetplates 49 joined by means of tie-rods 48 bolted at their ends, so that the cross-section of this set has the shape of a honeycomb.

What I claim is:

1. Process for the continuous concentration-crystallization of sugar syrups and massecuites by evaporation, said process comprising continuously subjecting syrups supplied to a series of successive crystallizing steps under the action of heating and boiling in several successive crystallizing massecuite recirculation circuits, introducing directly into the crystallizing massecuite, during each of the crystallizing steps except the first one, a damp air gaseous phase to ensure intense agitation and circulation of the said crystallizing massecuite in said successive recirculation circuits, separating the gaseous phase released by the massecuite at the top of each recirculation circuit, recycling by gravity the massecuite separated from the gaseous phase at the head of each recirculation circuit, so that each recirculation circuit has two liquid columns connected to its head and its base, the massecuite in one of said liquid columns having an upward movement caused by the thermic currents resulting from heating and from gaseous phase bubbles rising in said column, while the massecuite in the associated recycling column has a downward movement, interconnecting two successive circuits and discharging at the end of said successive crystallizing steps the product composed of nearly uniform crystalline grains in suspension in the resulting molasses.

2. Continuous concentration-crystallization process according to claim 1, wherein the gaseous phase is introduced into the crystallizing massecuite during the first concentrating-crystallizing step.

3. Continuous concentration-crystallization process according to claim 1, wherein each recirculation circuit is continuously supplied with crude preconcentrated sugar solutions to compensate for syrup spent by evaporation and crystallization.

4. Continuous concentration-crystallization process according to claim 1, wherein the gaseous bubbles of the upward flowing liquid column of the recirculation circuit are subjected to a forced dispersion during their rise in this column to reduce the average specific weight of the mixed liquid-gaseous phases and to increase the circulation force and to prevent hydraulic hammer effects in the circuit.

5. Continuous concentration-crystallization process according to claim 1, wherein crystalline seeds are introduced into the recirculation circuit during the first concentratingcrystallizing step in order to start the crystallization.

6. A device for the continuous concentrationcrystal lization of sugar syrups and massecuite comprising, in combination, a series of at least two vessel units, each one of which comprises a hollow column comprising means for introducing damp air into the column and having successively from the bottom to the top thereof a base-section, a heated enclosure connected to said base-section for generating a crystallizing mass, and an expansion chamber for the crystallizing mass arriving from said enclosure with which said expansion chamber communicates, and a set of substantially vertical partition walls for the forced dispersion of gaseous phase bubbles formed in the crystallizing mass below this set, a conduit ending in the basesection of said column, a gaseous/ liquid phases separating chamber interconnecting the top of said column and said conduit ending in the base-section of said column to recycle the crystallizing mass separated from the gaseous phase in the separating chamber, the said vessel units having an inlet for syrups to be treated, pipings interconnecting the conducts of two successive units to allow a free passage of the products from one unit to the next, a massecuite outlet on the last of said units, and a vapor and gas outlet at the head of each unit.

7. A continuous concentration-crystallization device according to claim 6, wherein the heated enclosure of each vessel unit comprises an intake and an outlet for enclosure heating fluid, upper and lower perforated plates forming respectively the cover and bottom of said enclosure, and a bundle of tubes fixed endwise in the holes of said perforated plates for connecting the base section and the expansion chamber of the corresponding column through said heated enclosure.

8. A continuous concentration-crystallization device according to claim 6, wherein the heated enclosure of each unit is located outside the corresponding column.

9. A continuous concentration-crystallization device according to claim 6, wherein each conduit to recycle the crystallizing mass is located outside the column of the corresponding unit and wherein said conduit forms with said column an O- or D-shaped circuit extended in the vertical direction.

10. A continuous concentration-crystallization device according to claim 6, wherein each conduit to recycle the crystallizing mass is located inside the column of the corresponding unit and wherein the lower orifice of this recycling conduit is located beneath the level of the heated enclosure through which said conduit passes.

11. A continuous concentration-crystallization device according to claim 6, wherein the set of substantially vertical partition walls in the column of each unit, for the forced dispersion of the gaseous phase bubbles in the crystalizing mass, comprises flat walls arranged in parallel, stayed and bolted tie-rods interconnecting said walls, and means for fixing said set at the top of the column and at the bottom of the gaseous/liquid phases separating cham ber of said unit.

12. A continuous concentration-crystallization device according to claim 6, wherein the set of substantially vertical partition walls in the column of each unit, for the forced dispersion of the gaseous phase bubbles in the crystallizing mass, comprises cylindrical walls having different diameters and arranged concentrically, and means for fixing said walls at the top of the column and at the bottom of the gaseous/liquid phases separating chamber of said unit.

13. A continuous concentration-crystallization device according to claim 6, wherein the means for introducing damp air into the column is located in the base-section of the column.

14. A continuous concentration-crystallization device according to claim 13-, wherein the means for introducing damp air comprises a perforated tray located beneath the inlet for the crystallizing mass recycled into the associated base-section, and an air-inlet located under this perforated tray.

15. A continuous concentration-crystallization device according to claim 6, wherein the means for introducing damp air into the column is located in the expansion chamber in the column.

16. A continuous concetitration-crystallization device according to claim 15, wherein the means for introducing damp air comprises a perforated tube forming bubbles, a source of air mixed with steam, and a feeding tube passing through the column Wall and interconnecting said source and said perforated tube.

References Cited UNITED STATES PATENTS 880,629 3/1908 Christianson 127-45 X 1,860,741 5/1932 Ieremiassen 12717 X 1,945,281 1/1934 Leith'auser 159l6 X 2,042,488 6/1936 Theiler 159-16 X 2,426,839 9/1947 Morris 209-139 X 3,266,556 8/1966 Malex 15916 FOREIGN PATENTS 1,104,869 11/1955 France.

OTHER REFERENCES Crystallizers, A. R. Thomson, Chemical Engineering, October 1950, pp. 125-132.

MORRIS O. WOLK, Primary Examiner D. G. CONLIN, Assistant Examiner U.S. Cl. X.R. 

